The method of the present invention is derived from a complex screening method (1) which relates to the oxidation and co-antioxidation of low density lipoprotein (LDL) lipids by a tocopherol-mediated mechanism (TMP, tocopherol-mediated peroxidation) (2). The latter mechanism summarizes a novel approach to explain the activity of .alpha.-tocopherol (.alpha.-TOH) in LDL in terms of both its ability to act as a phase transfer agent and also its role in the peroxidation of the lipid components of the lipoprotein. This earlier study (1) indicated that an effective co-antioxidant (XH) for .alpha.-TOH acted in three specific modes: the co-antioxidant must associate with an oxidizing LDL particle, reduce the lipid peroxidation chain carrying .alpha.-tocopheroxyl radical (.alpha.-TO.cndot.) [reaction 1], and the ensuing, co-antioxidant-derived radical (X.cndot.) must escape the lipoprotein particle (so as to minimize the possibility of regeneration of .alpha.-TO.cndot.) EQU XH+.alpha.-TO.cndot..fwdarw..alpha.-TOH+X.cndot. [1]
The co-antioxidant efficacy was evaluated previously by the corresponding anti-TMP index (1), where anti-TMP indices of approximately 0 referred to highly effective co-antioxidants, and anti-TMP indices of approximately 100 indicated poor co-antioxidant activities. As this methodology required the isolation and labour-intensive work-up of biological material we sought to develop a simple and rapid screen to identify potential co-antioxidants for .alpha.-TOH, based upon the ability of a test compound to reduce .alpha.-TO.cndot. which was compartmentalized from the surrounding aqueous medium.